Interrelations of markers of pubertal development and adolescent adjustment and behavior are investigated cross-sectionally and longitudinally. Participants are 9- to 14-year-old boys and girls and their parents who are seen at three times of measurement, six months apart. The markers of pubertal development include serum hormone levels, pubertal stage (Tanner criteria), and height and weight. Cortisol levels also were assessed, and menstrual history data were collected for the girls. Psychological assessments of the adolescent include adolescent- and parent-report of behavior problems and competencies and behavioral observations, including those of distress behaviors during a stressful procedure. Relations were found between cortisol levels and distress behavior during the most challenging situation sampled. Distress behaviors decreased across the year, but not all measures of cortisol showed decreases. Pattern of biological reactivity involving an increase, stability, or a decrease in cortisol level across samples at the first time of measurement differentially related to degree of reported behavior problems and ' depression symptoms in the adolescent one year later. Overlap of hormone levels for pre- and post-menarcheal girls as well as overlap of hormone levels for the various days of the menstrual cycle for menarcheal girls indicate that, in research on biobehavioral processes, menarche should be conceptualized as a process rather than as a discrete event. Self-reported menstrual history data indicate that "phase of the cycle" for many newly menarcheal girls also needs to be reconceptualized.